Liquid crystal display panel and liquid crystal display device

ABSTRACT

A pixel electrode ( 33 ), a gate bus line ( 31 ), and a source bus line ( 32 ) are formed while interposing an interlayer insulating film ( 35 ) therebetween. When viewed from the display surface side of a liquid crystal display panel, the pixel electrode ( 33 ), the gate bus line ( 31 ) and the source bus line ( 32 ) are arranged to overlap at least partially in the plan view. Consequently, in a liquid crystal display to which an OCB mode is applied, a uniform bend orientation can be attained over the entire screen even if transition nuclei are not generated in all pixels.

This application is the U.S. national phase of International ApplicationNo. PCT/JP2006/318689 filed 21 Sep. 2006 which designated the U.S. andclaims priority to Japanese Application No. 2006-034456 filed 10 Feb.2006, the entire contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a liquid crystal display panel and aliquid crystal display device, to each of which OCB (Opticallyself-Compensated Birefringence) mode is applied.

BACKGROUND ART

Various color liquid crystal displays are conventionally used as colordisplay devices having characteristics such as a flat shape andlightweight. As a liquid-crystal technology has been developed in recentyears, a color liquid crystal device having a high contrast and a wideviewing angle characteristic has been developed and widely put topractical use as a mainstream of a large-size display.

Such color liquid crystal display devices that are widely used thesedays adopt, for example, (i) a twisted nematic mode (hereinafterreferred to as a “TN mode”) in which an optical rotation of a liquidcrystal layer is controlled by an electrical field so that a display iscarried out, (ii) a birefringence mode (hereinafter referred to as an“ECB mode”) in which a birefringence of a liquid crystal layer iscontrolled by an electrical field so that a display is carried out, orthe like mode.

However, there is a problem in which the color liquid crystal displaydevice that uses these modes is not suitable for displaying moving imagebecause an image lag phenomenon occurs or an outline of image is blurreddue to a slow response speed.

In order to solve such a problem, many experiments for fastening aresponse speed of the color liquid crystal display have beenconventionally carried out. Currently, a ferroelectric liquid crystalmode, an antiferroelectric liquid crystal mode, an OCB mode, or the likehas been used as a liquid crystal mode having a fast response speed thatis suitable for moving image display.

There has been known that, in these modes, the ferroelectric liquidcrystal mode and the antiferroelectric liquid crystal mode have a lot ofproblems for practical uses because they have a low impact resistancedue to a layered structure.

On the other hand, the OCB mode has been focused as a liquid crystalmode suitable for moving image display because the OCB mode that uses ausual nematic crystal (i) has a strong impact resistance, (ii) isavailable in a wide temperature range, and (iii) has a wide viewingangel and a fast response characteristic.

FIG. 14 schematically illustrates the OCB mode. In a liquid crystaldisplay device to which the OCB mode is applied, a pair of transparentglass substrates 10 and 11 sandwich a liquid crystal layer 12therebetween, and transparent electrodes 13 and 14 are respectivelyprovided on the glass substrates 10 and 11 on a side of the liquidcrystal layer 12, and alignment films 15 and 16 are respectivelyprovided thereon. An alignment process is performed for the liquidcrystal layer 12 by rubbing.

In a case where a color display is carried out in the liquid crystaldisplay device, a color filter is provided on one of the glasssubstrates. In order that a liquid crystal is driven by active matrix, agate bus line and a source bus line are provided on the other one of theglass substrates, and a TFT is provided at an intersection thereof.After the substrates are respectively provided, the substrates arebonded via a spherical spacer or a column spacer so that an arbitral gapis provided therebetween. A liquid crystal is injected in vacuum betweenthe bonded substrates, or injected by a dropping method between thesubstrates when the glass substrates are bonded. In order that a viewingangle characteristic of display is improved, a wave plate (notillustrated) is bonded to either side or both sides of a liquid crystalcell, and a polarization plate (not illustrated) is externally bondedthereto.

The liquid crystal layer 12 that is right after the liquid crystal isinjected is often aligned as illustrated in FIG. 15, which is called aninitial alignment (splay alignment). When an intended voltage is appliedto the electrodes 13 and 14 that are respectively provided above andbelow the liquid crystal layer 12, an alignment transition occurs in theliquid crystal layer 12 and the alignment is gradually changed to analignment (bend alignment) illustrated in FIG. 14. When the liquidcrystal layer 12 becomes the bend alignment as illustrated in FIG. 14,an alignment change of the liquid crystal makes a response rapidly. Thisallows the fastest display in modes that use nematic crystal.Furthermore, when a wave plate is provided in the liquid crystal displaydevice, it is possible to realize a display state having a wide viewingangle characteristic.

As such, in the OCB mode, an alignment of a liquid crystal layer is asplay alignment while no voltage is applied, and a display is carriedout in a state where the alignment of the liquid crystal layer is in abend alignment. Consequently, in a liquid crystal display device towhich the OCB mode is applied, when a display is carried out, a voltageis continuously applied to a liquid crystal layer so that the bendalignment is maintained. For example, as illustrated in FIGS. 16 and 17,in a case where (i) a white display is carried out when a voltage V_(L)is applied, (ii) a black display is carried out when a voltage V_(H) isapplied, and (iii) an intermediate state is displayed when a voltagebetween V_(L) and V_(H) is applied, an alignment of the liquid crystallayer 12 is the bend alignment in a range of voltages V_(L) throughV_(H).

In the OCB mode, the liquid crystal layer 12 in the display statemaintains the bend alignment while a voltage is consistently applied,whereas the alignment of the liquid crystal layer 12 is the splayalignment while a power of the liquid crystal display device is in anOFF state and no voltage is applied. On this account, when the power ofthe liquid crystal display device is turned on, an alignment transitionfrom the splay alignment to the bend alignment (splay-to-bendtransition) occurs in the liquid crystal layer 12.

However, it is known that the splay-to-bend transition requires a highvoltage or a long time. It depends on a voltage applied to a liquidcrystal layer how long it takes that the splay-to-bend transition iscarried out over a screen. FIG. 18 illustrates how a voltage applied toa liquid crystal layer at room temperature (+25° C.) affects atransition time required for a splay-to-bend transition. In this case,an area of an electrode is 1 square centimeter (scm), and a cellthickness is 5 μm. As illustrated in FIG. 18, it is shown that, as thevoltage applied to a liquid crystal layer increases, the splay-to-bendtransition takes a shorter time.

Meanwhile, from observation of the splay-to-bend transition, it is shownthat the transition occurs from a peculiar place where several spacersare nucleated. Such a place is called a transition nucleus. Since merelyseveral transition nuclei may be generated in 1 scm, it takes longerthat the splay-to-bend transition spreads over the entire screen. Aspreading speed of the splay-to-bend transition depends on viscosity ofa liquid crystal. For example, the viscosity of a liquid crystal largelyincreases at low temperature such as −30° C. In this case, the spreadingspeed of the splay-to-bend transition becomes ten times slower that thatat room temperature.

Furthermore, in a practical TFT liquid crystal display panel, a pixelelectrode is provided in a region surrounded by a source bus line and agate bus line that are intersected with each other (hereinafter, both ofa source bus line and a gate bus line are referred to as just buslines). Generally, a distanced space is provided between the pixelelectrode and the bus lines for insulating the pixel electrode from thebus lines.

In the distanced space, a voltage is not sufficiently applied to theliquid crystal layer because there are no pixel electrode and bus lines.This is shown in FIG. 19. FIG. 19 illustrates an electric potential of aliquid crystal layer when a voltage is applied to pixel electrodes, buslines, and a counter electrode in a TFT liquid crystal display panel inwhich the pixel electrodes and the bus lines are provided in plane. Asapparent from FIG. 19, in distanced spaces between the pixel electrodesand the bus line, a voltage is not applied to the liquid crystal layer.

As such, in a distanced space where no voltage is applied to a liquidcrystal layer, even if a splay-to-bend transition occurs in a transitionnucleus in a certain pixel electrode, the splay-to-bend transition doesnot spread into adjoining pixel electrodes over the distanced spaces.From this reason, the splay-to-bend transition thus occurred in acertain pixel electrode does not spread into pixel electrodes having notransition nucleus therein, which causes a problem in which thesplay-to-bend transition does not spread over the entire screen.

In order to solve the problem, Patent Document 1 discloses anarrangement in which a convex section or a concave section made of aconductive material is provided at a specified position in a screen.With the arrangement, an electrical field intensity applied to a liquidcrystal layer on the convex or concave section becomes larger than asurrounding area, thereby promoting generation of transition nuclei.Thus, the transition nuclei are formed in each pixel, with the resultthat the splay-to-bend transition is easily carried out in all thepixels.

Patent Document 2 discloses driving means for generating a potentialdifference between a first electrode (for example, an auxiliarycapacitor electrode) and a second electrode (for example, a pixelelectrode) that is provided so as to overlap the first electrode via aninsulator and has a lacking section. With the arrangement, an electricalfield intensity applied to between the two electrodes becomes largerthan other regions, thereby resulting in that liquid crystal moleculespositioned around the lacking section become transition nuclei. Thisfacilitates a splay-to-bend transition to be carried out in all pixels.

In this way, in Patent Documents 1 and 2, all structures that are to betransition nuclei are provided in all pixels, so that, even if there aredistanced spaces in which no voltage is applied to a liquid crystallayer, a splay-to-bend transition occurs in all pixels, i.e., over anentire screen.

[Patent Document 1]

Japanese Unexamined Patent Publication, Tokukaihei, No. 10-20284(published on Jan. 23, 1998)

[Patent Document 2]

Japanese Unexamined Patent Publication, Tokukai, No. 2003-107506(published on Apr. 9, 2003)

DISCLOSURE OF INVENTION

However, in the conventional arrangements disclosed in Patent Documents1 and 2, the splay-to-bend transition may not occur in all pixels in thescreen depending on an operation environment or the like of the liquidcrystal display. For example, in a case of a low temperature such as−30° C., viscosity of the liquid crystal is too thick, so that thesplay-to-bend transition requires a longer time. In this case, enoughtransition nuclei required for an intended display may not be generated.

In addition, since all pixel electrodes and bus lines are notcontinuously provided in the TFT liquid crystal display panel due todistanced spaces provided therebetween, a splay-to-bend transition thathas occurred from transition nuclei in a certain pixel cannot spreadinto other pixels. This causes the following problem. That is, in a casewhere transition nuclei are not generated in all pixels, pixels in whichno transition nucleus is generated are not changed to the bendalignment, and remain as bright dots. Such the bright dots are observedas dot defects.

Furthermore, the arrangements of Patent Documents 1 and 2 have a problemin which additional processes for forming a structure to be transitionnuclei in a pixel are required in manufacturing the liquid crystaldisplay panel.

The present invention is accomplished in view of the above problems. Anobject of the present invention is to realize a liquid crystal displaydevice to which an OCB mode is applied, and in which a uniform bendalignment is attained over an entire screen even when transition nucleiare not generated in all pixels.

In order to solve the problems, a liquid crystal display panel of thepresent invention includes: an active matrix substrate including a pixelelectrode, a gate bus line, and a source bus line; and a countersubstrate provided so as to face the active matrix substrate via aliquid crystal layer whose alignment is changed from an initial state toan image display state having an alignment different from the initialstate, an interlayer insulating film being provided so as to insulatethe pixel electrode from the gate bus line and the source bus line, andthe pixel electrode being placed such that the pixel electrode, the gatebus line, and the source bus line, at least in part, overlap each otherin a planner manner, when viewed from a display surface side of theliquid crystal display panel.

Here, the liquid crystal layer whose alignment is changed from aninitial state to an image display state having an alignment differentfrom the initial state encompasses a liquid crystal layer in the OCBmode which is changed from a splay alignment (the initial state) to abend alignment (the image display state) while a power of the liquidcrystal display device is ON. In such a liquid crystal layer, itsalignment is changed from the initial state to the image display statewhen a voltage is applied to the liquid crystal layer. At this time, analignment transition occurs from transition nuclei and spreads over ascreen, with the result that the alignment transition is carried outover the entire screen.

In the arrangement, the interlayer insulating film is provided so as toinsulate the pixel electrode from the gate bus line and the source busline. While maintaining its insulation property, the pixel electrode isprovided such that the pixel electrode, the gate bus line, and thesource bus line, at least in part, overlap each other in a plane manner,when viewed from the display surface side.

With the arrangement, when the voltage is applied to the liquid crystallayer, a voltage-applied area can be continued between adjoining pixelelectrodes in a part where the pixel electrode overlaps the bus lines ina plane manner. As a result, an alignment transition that has occurredin a certain pixel can spread into its adjoining pixels, and also spreadinto pixels in which no transition nucleus is generated. This allows anentire screen to be changed to the image display state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view illustrating a pixel arrangement of a liquidcrystal display panel in accordance with Embodiment 1 of the presentinvention.

FIG. 2 is a cross sectional view taken along line A-A of FIG. 1.

FIG. 3 illustrates a potential state when a voltage is applied to pixelelectrodes, bus lines, and a counter electrode in the liquid crystalpanel of Embodiment 1.

FIG. 4 is a plan view illustrating a pixel arrangement of a conventionalliquid crystal panel.

FIG. 5 is a cross sectional view taken along line A-A of FIG. 4.

FIG. 6 is a plan view illustrating a pixel arrangement of a liquidcrystal display panel of Embodiment 2.

FIG. 7 is a cross sectional view taken along line B-B of FIG. 6.

FIG. 8 is a cross sectional view illustrating an arrangement of a liquidcrystal display panel of Embodiment 3.

FIG. 9 is a plan view illustrating a pixel arrangement of a liquidcrystal display panel as a modification example of the presentinvention.

FIG. 10 is a plan view illustrating a pixel arrangement of a liquidcrystal display panel as a modification example of the presentinvention.

FIG. 11 is a plan view illustrating a pixel arrangement of a liquidcrystal display panel as a modification example of the presentinvention.

FIG. 12 is a cross sectional view illustrating an exemplary position ofa contact hole in the liquid crystal display panel of Embodiment 3.

FIG. 13 is a cross sectional view illustrating another exemplaryposition of a contact hole in the liquid crystal display panel ofEmbodiment 3.

FIG. 14 is a cross sectional view illustrating a liquid crystal layerwhose alignment is a bend alignment, in a liquid crystal display deviceto which an OCB mode is applied.

FIG. 15 is a cross sectional view illustrating the liquid crystal layerwhose alignment is a splay alignment, in the liquid crystal displaydevice to which the OCB mode is applied.

FIG. 16 is a cross sectional view illustrating an exemplary alignment ofa liquid crystal during a white display.

FIG. 17 is a cross sectional view illustrating an exemplary alignment ofa liquid crystal during a black display.

FIG. 18 is a graph illustrating how a voltage applied to a liquidcrystal layer at room temperature affects a transition time required fora splay-to-bend transition.

FIG. 19 illustrates a potential state when a voltage is applied to pixelelectrodes, bus lines, and a counter electrode in a conventional liquidcrystal display panel.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 of the present invention is described below with referenceto FIGS. 1 through 5.

FIG. 1 is a plan view schematically illustrating a pixel arrangement ofa liquid crystal display panel of Embodiment 1. FIG. 2 is a crosssectional view taken along line A-A of FIG. 1.

As illustrated in FIGS. 1 and 2, the liquid crystal display panel is fora TFT liquid crystal display device, in which a liquid crystal layer 2is sandwiched between an active matrix substrate 3 and a countersubstrate 4.

The active matrix substrate 3 is arranged, in a schematic manner, suchthat a gate bus line 31, a source bus line 32, and a pixel electrode 33are provided on a substrate (e.g., a glass substrate) 30. In the activematrix substrate, a gate insulating film 34 is provided between the gatebus line 31 and the source bus line 32; an interlayer insulating film 35is provided so as to insulate the pixel electrode 33 from the gate busline 31 and the source bus line 32; and an alignment film 36 is providedon the pixel electrode 33. Further, a storage capacitor bus line 37 maybe provided in the same layer as the gate bus line 31.

The counter substrate is arranged such that a counter electrode 41 andan alignment film 42 are provided entirely on a substrate (e.g., a glasssubstrate) 40.

The pixel electrode 33 is connected to the gate bus line 31 and thesource bus line 32 via a TFT 50, while the pixel electrode 33 iselectrically connected to a drain electrode of the TFT 50 via a contacthole (not illustrated) provided in the interlayer insulating film 35.Moreover, the pixel electrode 33 is provided so as to cover the gate busline 31 and the source bus line 32 via the interlayer insulating film ina plane manner. That is, as illustrated in FIG. 1, when the liquidcrystal display panel is viewed from its display surface side, the pixelelectrode 33 is provided so as to overlap the bus lines, and nodistanced space is provided between the pixel electrode 33 and the buslines.

The following explanation deals with a specific example about how tomanufacture a liquid crystal display panel having the arrangements ofFIGS. 1 and 2. Firstly, an active matrix substrate (TFT array substrate)is formed as follows. A gate bus line 31 and a storage capacitor busline 37 are provided on a glass substrate 30 that is processed by a basecoat and the like. The gate bus line 31 and the storage capacitor busline 37 are formed in such a manner that a metal film is deposited allover the substrate 30 by sputtering, and the metal film is patterned bya photolithography process. The bus lines thus formed have a laminatedstructure constituted by Ta and its nitride, but may not necessarily besuch a laminated structure, and further, its material may be a metalsuch as Ti and Al, or ITO.

Then, surfaces of the gate bus line 31 and the storage capacitor busline 37 are anodized (not illustrated), and an insulating film 34 madeof silicon nitride or the like is further deposited thereon. It does notmake any difference whether the insulating film 34 may be patterned ornot.

Thereafter, a TFT 50 is formed in such a manner that (i) a semiconductorlayer is formed by a CVD method, (ii) the semiconductor layer ispatterned by a photolithography process, and (iii) an impurity isinjected therein so that a channel region of the TFT is formed. A metalfilm is deposited thereon by sputtering, and the metal film is patternedby a photolithography process so that a source bus line 32 and a drainelectrode are formed. A material of the source bus line 32 is a metalsuch as Ta, Ti, or Al, similarly to the gate bus line 31 and the storagecapacitor bus line 37. At the last, an insulting film is provided so asto cover the TFT 50 (not illustrated), thereby preventing diffusion ofthe impurity to the TFT section and increasing performance of thesemiconductor. In this way, the bus lines and the TFT section are formedin the TFT array substrate.

Then, an interlayer insulating film 35 is formed on the bus lines andthe TFT 50. The interlayer insulating film 35 is formed by use of aphotoresist made of a polymer material as follows. A photoresist isapplied to the TFT array substrate by spin coating, and the photoresistis exposed and developed for forming a contact hole on the drainelectrode in order that a pixel electrode is electrically conducted withthe drain electrode. The photoresist is then cured by burning in an ovenat around 180° C., and thus the interlayer insulating film 35 is formed.A film thickness of the cured interlayer insulating film 35 is 2 μm onaverage. As a material for the photoresist, either of a positive resistand a negative resist may be used. Then, a pixel electrode is formed insuch a manner that a metal film is deposited on the interlayerinsulating film 35 by sputtering, and the metal film thus deposited ispatterned by a photolithography process. A film thickness of the pixelelectrode is 140 nm.

The interlayer insulating film 35 is provided between the bus lines andthe pixel electrode 33 so that they are sterically spaced. Therefore,the pixel electrode 33 never short-circuits with the bus lines. On thisaccount, when the liquid crystal display panel is viewed from itsdisplay surface side, the pixel electrode 33 can be provided so as tooverlap a respective of the gate bus line 31 and the source bus line 32in a plane manner, and a space between each pixel electrode 33 can bearranged to be 5 μm. In this embodiment, the pixel electrode 33 is atransparent electrode made of ITO, but the pixel electrode 33 may bemade of a transparent thin-film conducting material such as IZO. In acase of a reflective liquid crystal display device, the pixel electrode33 may be made of a reflective thin-film conducting material such as Alor Ag instead of ITO.

The following explanation deals with a forming method of a countersubstrate. A counter substrate is formed as follows. A black matrix (notillustrated) for dividing each pixel and an RGB color filter (notillustrated) are formed on a glass substrate 40 in a stripe geometry.Then a transparent electrode 41 is formed in such a manner that ITO issputtered on the glass substrate 40.

Then, a process for aligning a liquid crystal on the TFT array substrateand the counter substrate is carried out. A polyimide for parallelalignment is printed on each of the substrates, and burned in an oven at200° C. for an hour, so that alignment films 36 and 42 are formed. Afilm thickness of each of the burned alignment films is around 100 nm.The alignment films are then rubbed with cotton in one direction so thatan alignment direction becomes parallel when the TFT array substrate andthe counter substrate are bonded with each other. An adequate amount ofplastic spacers of 5 μm in diameter are sprayed on the TFT arraysubstrate by a dry method, while a seal is printed on a peripheralregion of a screen in the counter substrate. Then the substrates arebonded in place with each other. A thermosetting resin is used as theseal. The substrates thus bonded are then burned in an oven at 170° C.for one and a half hours under pressure. A liquid crystal is injectedbetween the substrates by use of a vacuum injection method. In this way,the liquid crystal display panel of the Embodiment 1 is formed.

Moreover, for the sake of a wide viewing angle, a viewing anglecompensation wave plate is provided on either side of the liquid crystaldisplay panel, and a polarization plate is further provided on theeither side of the liquid crystal display panel such that absorptionaxes of the wave plates and the polarization plates are orthogonal toeach other.

In a liquid crystal display device having the arrangements of FIGS. 1and 2, a potential when a voltage was applied to the pixel electrode 33,the bus lines, and the counter electrode 41 was measured. The result isshown in FIG. 3. In the liquid crystal display device, since the pixelelectrode 33 was provided so as to overlap the bus lines via theinterlayer insulating film 35 in a plane manner, no distanced spaced wasprovided between the pixel electrode and the bus lines. As a result, asshown in FIG. 3, it is shown that the voltage was sufficiently appliedto between each of the pixel electrodes adjoining each other.

Then, an optical characteristic of the liquid crystal display panel thusmanufactured by the above method was evaluated. Ten volts were appliedto the liquid crystal layer in such a manner that a signal of 0V wassupplied from the source bus line to the pixel electrode, and analternating current rectangular wave of 10V was applied to the counterelectrode. After a period of time when the voltages were applied, asplay-to-bend transition spread over an entire screen, and all pixelswere changed to a bend alignment. In the other words, in the liquidcrystal display panel of Embodiment 1, since the pixel electrode wasprovided so as to overlap the bus lines in a plane manner, it wasobserved that the splay-to-bend transition was not only carried out inone pixel, but also spread into adjoining pixels.

In the liquid crystal display panel, since the screen was entirelychanged to the bend alignment, a black state was observed from anoblique direction by use of the viewing angle compensation wave platesin combination, thereby realizing a liquid crystal display panel havinga wide viewing angle characteristic. Furthermore, even when the voltagewas quickly switched between ON and OFF, a rapid response in not morethan a few msec was demonstrated. Here, the ON means a comparativelyhigh voltage corresponding to a black display, and the OFF means acomparatively low voltage corresponding to a white display. For example,a voltage of 10V is ON, and a voltage of 2 V is OFF.

For comparison, a TFT liquid display panel having a conventionalstructure in which no interlayer insulating film is provided between buslines and a pixel electrode was manufactured. FIG. 4 is a plan viewillustrating a pixel arrangement of a comparative TFT liquid crystaldisplay panel. FIG. 5 illustrates a cross sectional view take along lineA-A of FIG. 4. In FIGS. 4 and 5, constituent members similar to those inFIGS. 1 and 2 have the same referential numerals as those in FIGS. 1 and2.

In the conventional TFT liquid crystal display panel, since nointerlayer insulating film is provided between a pixel electrode 33 andbus lines, the pixel electrode 33 cannot be provided so as to overlapthe bus lines in a plane manner. From this reason, for the sake ofpreventing short-circuit of the pixel electrode 33 with the bus lines, aspace is provided so as to be 5 μm between the bus lines and the pixelelectrode.

In a similar manner to the above method, a conventional liquid crystaldisplay panel was manufactured, and observed in a state where ten voltswere applied to the liquid crystal layer. In the liquid crystal displaypanel, because a splay-to-bend transition did not spread into adjoiningpixels, there remained pixels that were not changed to a bend alignment.As a result, when viewed from an oblique direction, the pixels wereobserved as bright dots due to a difference of retardation. This may bebecause the voltage was not sufficiently applied to a part of the liquidcrystal layer between the pixel electrode and the bus lines, and thepart of the liquid crystal layer disturbed spread of the splay-to-bendtransition. Accordingly, it is considered that the liquid crystal couldnot be changed to the bend alignment at all in pixels having notransition nucleus. These pixels that were not changed to the bendalignment remained during displaying and were never changed to the bendalignment.

EMBODIMENT 2

Embodiment 2 of the present invention is described below with referenceto FIGS. 6 and 7.

The following explanation deals with a TFT liquid crystal display panelof Embodiment 2 with reference to FIGS. 6 and 7. FIG. 6 is a plan viewschematically illustrating a pixel arrangement of a liquid crystaldisplay panel of Embodiment 2. FIG. 7 is a cross sectional view takenalong line A-A of FIG. 6. In FIGS. 6 and 7, constituent members similarto those in FIGS. 1 and 2 have the same referential numerals as those inFIGS. 1 and 2.

A TFT liquid crystal display panel of Embodiment 2 has an arrangementalmost similar to the liquid crystal display panel of Embodiment 1, butis different from that of Embodiment 1 in that a pixel electrode 33includes an opening section 33A at a part of an intersection of a pixelelectrode 33 and a storage capacitor bus line 37. The TFT liquid crystaldisplay panel of Embodiment 2 can be manufactured by use of the samematerials as the liquid crystal display panel of Embodiment 1.

In the TFT liquid crystal display panel of Embodiment 2, the openingsection 33A may be formed when a pixel electrode is patterned by aphotolithography process. This makes it possible to manufacture the TFTliquid crystal display panel of Embodiment 2 without any additionalprocesses compared with the case of manufacturing the liquid crystaldisplay panel of Embodiment 1.

An optical characteristic of the liquid crystal panel thus manufacturedby the above method was evaluated. Ten volts were applied to a liquidcrystal layer in such a manner that a signal of 0V was supplied from asource bus line to a pixel electrode, and an alternating currentrectangular wave of 10V was applied to an electrode of a countersubstrate. Furthermore, 10V of an alternating current rectangular wavehaving a polarity opposite to the counter electrode were applied to astorage capacitor bus line. Accordingly, a voltage of 10V or more wasapplied to the liquid crystal layer between the storage capacitor busline and the counter electrode, and a voltage of a few volts was appliedto between the storage capacitor bus line and the pixel electrode. Aftera period of time when the voltages were applied, a splay-to-bendtransition spread over an entire screen, and all pixels were changed toa bend alignment. A time required for the splay-to-bend alignment wasshortened by half compared with Embodiment 1.

This may be because, in the TFT liquid crystal display device ofEmbodiment 2, the voltage that was greater than usual was applied tobetween the counter electrode 41 and the storage capacitor bus line, sothat more transition nuclei were generated compared with Embodiment 1,thereby causing the splay-to-bend transition rapidly.

Moreover, another possible reason may be as follows. The voltage wasapplied to between the pixel electrode 33 and the storage capacitor busline 37 that were provided via a thin interlayer insulating film 35, sothat its electrical field promoted changes in liquid crystal moleculesand caused transition nuclei to be generated in the liquid crystallayer. As a result, the splay-to-bend transition could be carried outrapidly. That is, the electrical field generated, around the openingsection 33A, between the storage capacitor bus line 37 and the pixelelectrode 35 is not only in a vertical direction, but also in a lateraldirection, i.e., a lateral electrical field that passes through theliquid crystal layer 2 generates between the storage capacitor bus line37 and the pixel electrode 35. This can cause a twist alignment in theliquid crystal. The twist alignment thus caused, around the openingsection 33A, in the liquid crystal can cause the splay-to-bendtransition.

Furthermore, it was also observed in the TFT liquid crystal displaydevice of Embodiment 2 that the splay-to-bend transition spread intopixels in which no transition nucleus was generated. This is because thepixel electrode was provided so as to overlap the bus lines in a planemanner. Since a screen was entirely changed to the bend alignment, ablack state was observed from an oblique direction by use of viewingangle compensation wave plates in combination, thereby realizing aliquid crystal display panel having a wide viewing angle characteristic.Furthermore, even when the voltage was quickly switched between ON andOFF, a rapid response in not more than a few msec was demonstrated.

EMBODIMENT 3

Embodiment 3 of the present invention is described below with referenceto FIGS. 8 and 12. The following explanation deals with a TFT liquidcrystal display panel of Embodiment 3 with reference to FIG. 8. A planarstructure of a pixel of a liquid crystal display panel of Embodiment 3is the same as that of FIG. 6. FIG. 8 is a cross sectional view takenalong line B-B of FIG. 6. In FIG. 8, constituent members similar tothose in FIGS. 6 and 7 have the same referential numerals as those inFIGS. 6 and 7.

A TFT liquid crystal display panel of Embodiment 3 has an arrangementalmost similar to the liquid crystal display panel of Embodiment 2, butis different from that of Embodiment 2 in that, as illustrated in FIG.8, an opening section 35A is provided in an interlayer insulating film35 at a position where an opening section 33A is provided in a pixelelectrode 33, the opening section 35 being formed in such a manner thata part of the inter layer insulating film 35 is removed. The openingsection 35A in the interlayer insulating film 35 is wider in some degreethan the opening section 33A in the pixel electrode 33. The TFT liquidcrystal display panel of Embodiment 3 can be manufactured by use of thesame materials as the liquid crystal display panels of Embodiments 1 and2.

In the TFT liquid crystal display panel of Embodiment 3, the openingsection 35A can be formed simultaneously in an exposure and developmentprocess in which a contact hole is formed in the interlayer insulatingfilm 35 that is formed of a photoresist. This makes it possible tomanufacture the liquid crystal display panel of Embodiment 3 without anyadditional processes compared with the case of manufacturing the liquidcrystal display panel of Embodiment 1.

An optical characteristic of the liquid crystal panel thus manufacturedby the above method was evaluated. Ten volts were applied to a liquidcrystal layer in such a manner that a signal of 0V was supplied from asource bus line to a pixel electrode, and an alternating currentrectangular wave of 10V was applied to an electrode of a countersubstrate. Furthermore, 100V of an alternating current rectangular wavehaving a polarity opposite to the counter electrode were applied to astorage capacitor bus line. Thus, a voltage of around 20V was applied tothe storage capacitor bus line and the counter electrode, and a voltageof around 10V was applied to the storage capacitor bus line and thepixel electrode. After a period of time when the voltages were applied,a splay-to-bend transition spread over an entire screen, and all pixelswere changed to a bend alignment. A time required for the splay-to-bendalignment was shortened by one tenth compared with Embodiment 1.

This may be because, in the TFT liquid crystal display device ofEmbodiment 3, the voltage greater than usual was applied to between thecounter electrode and the storage capacitor bus line, so that moretransition nuclei were generated, thereby causing the splay-to-bendtransition more rapidly.

Moreover, another possible reason may be as follows. The voltage wasapplied to between the pixel electrode 33 and the storage capacitor busline 37 that were provided via a thin gate insulating film 34, so thatits electrical field promoted changes in liquid crystal molecules andcaused transition nuclei to be generated in the liquid crystal layer. Asa result, the splay-to-bend transition could be carried out morerapidly. That is, the electrical field generated, around the openingsection 33A, between the storage capacitor bus line 37 and the pixelelectrode 35 is not only in a vertical direction, but also in a lateraldirection, i.e., a lateral electrical field that passes through theliquid crystal layer 2 generates between the storage capacitor bus line37 and the pixel electrode 35. This can cause a twist alignment in theliquid crystal. Here, in Embodiment 3, since only the gate insulatingfilm 34 is provided between the pixel electrode 33 and the storagecapacitor bus line 37 in the opening section 35A that is formed byremoving the interlayer insulating film 35, an intensity of the lateralelectrical field is greater than that in Embodiment 2, thereby causingthe splay-to-bend alignment more easily.

Furthermore, it was also observed in the TFT liquid crystal displaydevice of Embodiment 3 that the splay-to-bend transition spread intopixels in which no transition nucleus was generated. This is because thepixel electrode was provided so as to overlap the bus lines in a planemanner. Since a screen was entirely changed to the bend alignment, ablack state was observed from an oblique direction by use of viewingangle compensation wave plates in combination, thereby realizing aliquid crystal display panel having a wide viewing angle characteristic.Furthermore, even when the voltage was quickly switched between ON andOFF, a rapid response in not more than a few msec was demonstrated.

In the liquid crystal display panel of Embodiment 3, it is also possibleto form the gate insulating film 34 and the interlayer insulating film35 at the same time instead of forming them separately. In this case, ifno insulating film is provided in a lacking section (corresponding tothe opening section 35A of FIG. 8) provided at an intersection of thestorage capacitor bus line 37 and the pixel electrode 33, the upper andlower electrodes are electrically conducted with each other. From thisreason, it is necessary to provide an insulating film in the lackingsection. A method for providing an insulating film in the lackingsection encompasses (1) a method in which an insulating film is formedof a material using a resist, and an exposure process is not fullycarried out (half exposure), and (2) a method in which etching of aninsulating film is ceased in the middle of the process. These methodsare known as methods that are difficult to be repeated or controlled,but if these methods are possible, then it is advantageously possible toshorten a process for forming an insulating film.

In each of the liquid crystal display panels described in Embodiments 1through 3, the pixel electrode 33 is arranged such that a periphery ofthe pixel electrode 33 almost entirely overlaps the bus lines in a planemanner. Even in a case where a periphery of the pixel electrode 33, onlyin part, overlaps the bus lines in a plane manner, as illustrated inFIGS. 9 through 11, it is also possible to obtain an advantageouseffect.

For example, in arrangements of FIGS. 9 and 10, since a splay-to-bendtransition surely spreads in a vertical or lateral direction, it is notnecessary that transition nuclei be generated in all pixels. However, itis further preferable to ensure the splay-to-bend transit spreads infour directions. On this account, it is preferable that four sides ofthe pixel electrode 33 respectively overlap, in part, the bus lines in aplane manner as illustrated in FIG. 11.

Moreover, in the aforementioned liquid crystal display panel ofEmbodiment 3, a contact hole for connecting the pixel electrode 33 to adrain electrode of a TFT 50 is generally provided close to the drainelectrode, as illustrated in FIG. 12. However, it is also possible, asillustrated in FIG. 13, to use a part where the interlayer insulatingfilm 35 is removed at the intersection of the storage capacitor bus line37 and the pixel electrode 33 as the contact hole to the drainelectrode. In this case, since the contact hole is not required to beformed at a different position, it is possible to increase an apertureratio of the pixel. With the arrangement in FIG. 13, the aperture ratiois increased, so that a transmittance of the panel is improved andconsequently an amount of backlight can be restrained. This makes itpossible to realize a liquid crystal display panel with low powerconsumption.

Furthermore, a liquid crystal display device is realized in such amanner that a driving circuit, a backlight (light source), or the likeis provided to the liquid crystal display panel in accordance withEmbodiments 1 through 3.

As described above, a liquid crystal display panel of the presentinvention includes an active matrix substrate including a pixelelectrode, a gate bus line, and a source bus line, and a countersubstrate are provided so as to face the active matrix substrate via aliquid crystal layer whose alignment is changed from an initial state toan image display state having an alignment different from the initialstate, an interlayer insulating layer being provided so as to insulatethe pixel electrode from the gate bus line and the source bus line, andthe pixel electrode being provided such that the pixel electrode, thegate bus line, and the source bus line overlap each other in a planemanner, when viewed from a display surface side of the liquid crystaldisplay panel.

Here, the liquid crystal layer whose alignment is changed from aninitial state to an image display state having an alignment differentfrom the initial state encompasses a liquid crystal layer in the OCBmode which is changed from a splay alignment (the initial state) to abend alignment (the image display state) while a power of the liquidcrystal display device is ON. In such a liquid crystal layer, itsalignment is changed from the initial state to the image display statewhen a voltage is applied to the liquid crystal layer. At this time, analignment transition occurs from transition nuclei and spreads over ascreen, with the result that the alignment transition is carried outover the entire screen.

In the arrangement, the interlayer insulating layer is provided so as toinsulate the pixel electrode from the gate bus line and the source busline. While maintaining its insulation property, the pixel electrode isprovided such that the pixel electrode, the gate bus line, and thesource bus line, at least in part, overlap each other in a plane manner,when viewed from the display surface side.

With the arrangement, when the voltage is applied to the liquid crystallayer, a voltage-applied area can be continued between adjoining pixelelectrodes in a part where the pixel electrode overlaps the bus lines ina plane manner. As a result, an alignment transition that has occurredin a certain pixel can spread into its adjoining pixels, and also spreadinto pixels in which no transition nucleus is generated. This allows theentire screen to be changed to the image display state.

Moreover, the liquid crystal display panel can be further include: astorage capacitor bus line so that the interlayer insulating layer isprovided between the pixel electrode and the storage capacitor bus line;and an opening section being provided partially the pixel electrode in aregion where the pixel electrode and the storage capacitor bus line areintersected with each other.

With the arrangement, a lateral electrical field is generated, aroundthe opening section, between the storage capacitor bus line and thepixel electrode, and the lateral electrical field causes a twistalignment in a liquid crystal. This causes transition nuclei to begenerated in many pixels, with the result that a rapid alignmenttransition from the initial state to the image display state is attainedin the liquid crystal layer.

Furthermore, the liquid crystal display panel can be arranged such thatthe interlayer insulating film provided around the opening section has afilm thickness thinner than that in other region.

With the arrangement, the lateral electrical field generated around theopening section becomes large, thereby resulting in that the alignmenttransition from the initial state to the image display state can becarried out more rapidly in the liquid crystal layer.

The liquid crystal display panel can be arranged such that the liquidcrystal layer is a liquid crystal layer in an OCB mode.

The liquid crystal display panel can be arranged such that the pixelelectrode is a transparent electrode.

1. A liquid crystal display panel, comprising: an active matrixsubstrate including a pixel electrode, a gate bus line, and a source busline; a counter substrate provided so as to face the active matrixsubstrate via a liquid crystal layer whose alignment is changed from aninitial state to an image display state having an alignment differentfrom the initial state; and an interlayer insulating film provided so asto insulate the pixel electrode from the gate bus line and the sourcebus line, the pixel electrode being provided such that the pixelelectrode, the gate bus line, and the source bus line, at least in part,overlap each other in a plane manner, when viewed from a display surfaceside of the liquid crystal display panel an opening section beingprovided partially in the pixel electrode in a region where the pixelelectrode and the storage capacitor bus line are intersected with eachother.
 2. The liquid crystal display panel as set forth in claim 1,further comprising: a storage capacitor bus line provided so that theinterlayer insulating film ha-y˜ is provided between the pixel electrodeand the storage capacitor bus line.
 3. The liquid crystal display panelas set forth in claim 2, wherein: the interlayer insulating filmprovided around the opening section has a film thickness thinner thanthat in other region.
 4. The liquid crystal display panel as set forthin claim 1, wherein: the liquid crystal layer is a liquid crystal layerin an OCB mode.
 5. The liquid crystal display panel as set forth inclaim 1, wherein: the pixel electrode is a transparent electrode.
 6. Aliquid crystal display device comprising a liquid crystal display panelas set forth in claim 1.